Английский язык для судовых электромехаников - [16]
26 7
Prepare a) short talk with your fellow-student on basic electrical measuring instruments. Use ex. 24, 25. Then record your dialogue.
27 4
Solve these two problems.
1. Suppose the ammeter scales reads 1.9 amp., the voltmeter scale reads 2.4. V. How much is the value of resistance in the measured circuit?
2. Suppose the ohmmeter scale reads 75 ohms, the voltmeter scale reads 220 V. How much is the value of current in the measured circuit?
28 9
Practice pronunciation. Open your books and repeat after the speaker in pauses 3 paragraphs of the recorded text “Basic Electrical Measuring Instruments”. Thea close your books and do the same with paragraphs 4—7.
29 1
What is the name of this device?
This device measures the frequency of alternating current. It consists of a tuned circuit calibrated in frequencies. It can show maximum current when; the tuned frequency of the circuit is the same as the frequency of the voltage or current being measured.
30 6
After listening to two texts say what differs them and what they have in common.
Capacitors
The capacity of a capacitor is measured in farads. A capacitor has a capacity of 1 farad when a charge of 1 coulomb increases the potential, between its plates, by 1 volt.
The capacity depends on four things: a) the higher the voltage used to charge the capacitor the more energy it will store; b) the larger the size; of plates and the greater their number the more energy will be stored; c) the closer are the positive an.d negative plates the greater is the charge; d) some insulators store greater charge than others.
Capacitor in A-C Line
When a capacitor is connected into a circuit through which alternating current is flowing, the plates of the capacitor are charged negatively or positively.
In order to show the action of a capacitor in an a-c line, connect a capacitor in series with a lamp and plug into the a-c lighting. The lamp will glow provided its resistance does not prevent. Then connect another capacitor in parallel and the lamp will glow brighter. Connecting more capacitors and increasing the capacity we increase the glow.
Thus, capacitors oppose the flow of current.
31 20
Home exercise. Write your recommendations on general requirements to lighting and be prepared to dwell on the subject provided by the text.
Lighting. General Requirements.
In all rooms, spaces and locations' of the ship where lighting is necessary to ensure the safety of navigation, operating of machinery and equipment, as well as accommodating and evacuation of passengers and crew, stationary fixtures>1 of main lighting are to be installed.
Lighting fixtures installed in rooms and spaces, where mechanical damage is possible to the glass hoods>2 are to be provided with' protecting gratings>3.
Lighting fixtures are to be installed in such a manner as to prevent; heating of cables and adjacent materials up to a temperature exceeding the permissible>4 level.
Permanently-installed lighting fixtures in holds are to take their power supply from a special switchboard. Apart from the fuses and switches this switchboard is to be provided with visual signals to monitor individual lighting circuits.
In rooms or places illuminated with luminiscent lamps where visible rotating parts of machinery are located, all measures to be taken to prevent stroboscopic effect.
When using d-c, a label indicating the voltage level is to be fitted on switchboards feeding the discharge lamps.
>1 арматура, >2 колпак, >3 решетки, >4 допустимый
32 15
Ноте exercise. Check your reading skills,
a) Read the text.
Special Meters
Thermocouple meters (Fig. 2) convert applied current (a-c or d-c) by thermoelectric effects into deflection currents which register on a PM moving-coil couple actuated by heat generated at the junction formed by two strips of dissimilar metal. One strip carries the heat-generating input currents, the other carries heat-produced currents to the meter movement.
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Thermocouple meters are used to measure a wide range of either a-c or d-c currents and give an accurate picture of the effective, or heat-j producting, value of a current noi matter what its nature. The meters are relatively expensive and the thermal delay in converting input electricity to heat makes them sluggish.
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| Fig. 2. Arrangement of thermocouple meters |
b) Place a transparent film on the text and insert every fifth word (22) which is shaded on the film.
c) Fill in the blanks in such a way that it makes sense.
1. The convertion of applied current into deflection current is through a thermocouple.... a) actuated by two strips of dissimilar metal; b) actuated by heat generated at the junction; c) generated by input currents.
2. Thermocouple meters are used to... . a) measure voltage by the comparison method; b) operate through the electrostatic repulsion;
c) measure a wide range of either a-c or d-c currents.
3. Thermocouple meters are relatively. ... a) expensive; b) large;
c) cheap.
Now record your time and results 22—20 correctly inserted words+3 correct answers per 8 minutes get you an excellent mark.
